Image sensors are semiconductor devices capable of converting optical images into electric signals. The image sensor may be classified into two types: a charge coupled device (CCD) type and a complementary metal-oxide-semiconductor (CMOS) type. The CMOS type image sensor (CIS) may include a plurality of pixels two-dimensionally arranged. Each of the pixels may include a photodiode (PD) that converts incident light into an electrical signal.
As an integration density of the image sensor increases, a size of each pixel in the image sensor decreases, which can lead to a reduction in full well capacity of each photodiode.